Question

Exercise 10.3 Cholera This exercise looks at the symptoms of cholera and how the bacterium causes them. Cholera is often treated by oral rehydration therapy (ORT), and this exercise should also help you to gain an understanding of how this works and the ethics of testing new therapies. 1 The cholera bacterium, Vibrio cholero, releases a toxin that causes intestinal epithelial cells to actively pump out chloride ions into the lumen of the intestine. This causes water loss from the blood and intestinal epithelial cells. This is shown in Figure 10.6. C- Na+H20 cholera toxin O CFTR adenylate cyclase CAMP 3Na Figure 10.6 The action of cholera toxin on intestinal cells. Use your knowledge of osmosis to explain why cholera infection leads to dehydration. 2 People infected by cholera suffer from severe diarrhoea, which causes dehydration. In an effort to rehydrate patients, they are often given oral rehydration salt solutions to drink. These solutions consist of a mixture of ions and glucose measured out in carefully controlled concentrations. Figure 10.7 shows a packet of oral rehydration therapy

Answer 1

1. Osmosis refers to the movement of solvent particles from the region of their high chemical potential gradient to the region of a low chemical potential gradient.

In the given case, the solvent is water.
Water potential refers to the kinetic energy associated with free water molecules.
Water potential = Solute potential + Pressure potential
The presence of solutes reduces the water potential.

In the given case, the presence of solutes i.e. chloride ions in the intestinal lumen reduces the water potential in the lumen. This results in the exosmosis of water from the surrounding cells into the lumen.
As a result, a large amount of water is lost through stool.
i.e. Dehydration